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Abstract Cirsium ownbeyi(Ownbey’s thistle) is a regional endemic of northeastern Utah, northwestern Colorado, and southwestern Wyoming and was formerlya Category 2 candidate for listing under the Endangered Species Act. Prior to 1998, it was known from only two locations in Wyoming and was considered a high priority species of special concern. Surveys in 1998 relocated both known occurrences and resulted in the discovery of five new populations. The state population is currently estimated at 56,000-74,000 plants in about 100 acres of occupied habitat. C. ownbeyi typically occurs in sparsely vegetated openings on slopes and ridgetops within a matrix of sagebrush grasslands on whitish to reddish limey slate derived from the Green River Formation. Although most populations are secure at present, some sites could be negatively impacted by heavy recreation use by off-road vehicles or weed control programs using broadleaf herbicides. Five populations are found on BLM lands in Sweetwater County, including two on designated ACECs. Although not recommended for federal listing under the Endangered Species Act, C. ownbeyiis restricted enough in its habitat requirements and range that it should be considered “sensitive” during BLM resource management planning.

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Abstract Cirsium ownbeyi(Ownbey’s thistle) is a regional endemic of northeastern Utah, northwestern Colorado, and southwestern Wyoming and was formerlya Category 2 candidate for listing under the Endangered Species Act. Prior to 1998, it was known from only two locations in Wyoming and was considered a high priority species of special concern. Surveys in 1998 relocated both known occurrences and resulted in the discovery of five new populations. The state population is currently estimated at 56,000-74,000 plants in about 100 acres of occupied habitat. C. ownbeyi typically occurs in sparsely vegetated openings on slopes and ridgetops within a matrix of sagebrush grasslands on whitish to reddish limey slate derived from the Green River Formation. Although most populations are secure at present, some sites could be negatively impacted by heavy recreation use by off-road vehicles or weed control programs using broadleaf herbicides. Five populations are found on BLM lands in Sweetwater County, including two on designated ACECs. Although not recommended for federal listing under the Endangered Species Act, C. ownbeyiis restricted enough in its habitat requirements and range that it should be considered “sensitive” during BLM resource management planning.

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